Concept:An interaction in which both organisms benefit is called mutualism.Explanation:Mutualism is a close association between two organisms where both partners benefit from the relationship.In commensalism, only one organism benefits while the other is neither helped nor harmed.Saprophytism involves organisms feeding on dead organic matter, not a mutually beneficial association.Symbiosis is a broad term covering interactions that may not benefit both organisms, such as parasitism.Answer:B. Mutualism